The present invention relates generally to communication networks and more specifically to systems and methods for shaping network traffic in a queuing hierarchy using link fragmentation and interleaving.
High speed networks are designed to carry services with a wide range of quality-of-service (QoS) requirements. It is useful to define a hierarchy of traffic classes over which QoS requirements may be configured. FIG. 1 depicts an example of such a hierarchy. There are three levels. The bottom level or root is a node 102 defining a physical interface over which traffic will be transmitted. The physical layer represents all physical layer entities, such as Ethernet ports, TDM channels, POS ports, clear channel ports, etc. The next level of hierarchy shows three logical interfaces 104, 106, 108. The logical layer represents those interfaces that have virtual circuits, such as frame relay (FR) or virtual LANs (VLANs). A third level of hierarchy consists of classes. Here logical interface 104 has associated classes 110 and 112. Logical interface 106 has classes 114, 116, and 118. Logical interface 108 has associated classes 120 and 122. The class layer contains packet queues where packets are queued awaiting transmission. Each class may represent, for example, a different customer.
Thus, all of the classes, logical interfaces, and physical interfaces are represented by nodes in a tree structure. The nodes corresponding to the classes are leaf nodes, i.e., they are furthest from the root node in the hierarchy. When packets arrive they are placed in a queue associated with a leaf node. Individual nodes can be configured as priority nodes. In FIG. 1, priority nodes are drawn with dashed lines. Priority nodes have higher scheduling preference than their siblings regardless of the other scheduling criteria. For example, voice traffic may be assigned to a priority class.
Link Fragmentation and Interleaving (LFI) is a method used on low speed interfaces to allow higher priority traffic to move ahead or be interleaved with lower priority traffic. Large packet size, lower priority traffic is typically fragmented into smaller chunks in order to provide opportunities for higher priority traffic to be injected into the packet stream.
In conventional systems, the fragmentation and interleaving function was performed in software and a physical framer had no knowledge that LFI was being performed. Thus, from a software perspective, a single physical interface was used and flow control was represented as a single entity. More recently developed framer chips have incorporated some of the LFI functionality into hardware. These framers now represent the single physical interface as two separate interfaces: one for high priority traffic (non-fragmented), which is to be interleaved with the lower priority traffic, and the second interface for low priority traffic which will be fragmented into smaller chunks. While this offers several advantages over software, it introduces a new problem that software must solve and that is the management of flow control and physical interface shaping across two interfaces.
There is, therefore, a need for a method and system which allows multiple traffic flows to be shaped as if they were a single flow while designating one of the flows to be unrestricted.